Generally speaking, this invention relates to a process for producing miniaturized pressure transducers, and, more particularly, to the preparation of such transducers which will tolerate elevated temperatures in use. Such transducers are of the kind which have a diaphragm which is contoured to concentrate and control the induced stress in the areas of the piezoresistor gauges, and to direct stresses to the gauges so as to sense, in the areas where the transducers are mounted, differentiations in pressure. More particularly, this invention relates to a process for producing silicon diaphragm pressure transducers or semiconductors, and to pressure transducers or semiconductors so produced, by utilizing two specifically oriented silicon wafers which are joined together by diffusion techniques which use reduced and less costly operating parameters. The resulting transducers and/or semiconductors have a gauge film surface which is rich in boron, extremely level, and extraordinarily uniform throughout the extent thereof.
The art of fabricating pressure transducers by diffusing piezoresistor gauges into a silicon diaphragm is well known. In this connection, reference is made to U.S. Pat. No. 4,065,970 issued Jan. 3, 1978, which is hereby incorporated by reference in its entirety wherein a single silicon wafer is utilized. Also, reference is made to U.S. Pat. No. 3,858,150, issued Dec. 31, 1974 wherein a multilayered silicon wafer arrangement is disclosed. The problem with prior art devices is that they do not provide proper insulation of the strain gauges from the diaphragm which is exposed to elevated temperatures. Therefore, the pressure transducer fails upon being exposed to elevated temperatures commonly achieved in industrial practice.
With this invention, by contrast, a simplified process is provided for formulating silicon diaphragm pressure transducers or semiconductors which will operate in high temperature applications above 150.degree. C., the usual maximum temperature for such devices, and which process is simplified and easily carried out utilizing processing temperatures and pressures which are at a much lower level, then previously achieved, which makes the process herein much more appropriate for mass production techniques.